Loss of SIRT1 inhibits hematopoietic stem cell aging and age-dependent mixed phenotype acute leukemia

Aging of hematopoietic stem cells (HSCs) is linked to various blood disorders and malignancies. SIRT1 has been implicated in healthy aging, but its role in HSC aging is poorly understood. Surprisingly, we found that Sirt1 knockout improved the maintenance of quiescence of aging HSCs and their functionality as well as mouse survival in serial bone marrow transplantation (BMT) recipients. The majority of secondary and tertiary BMT recipients of aging wild type donor cells developed B/myeloid mixed phenotype acute leukemia (MPAL), which was markedly inhibited by Sirt1 knockout. SIRT1 inhibition also reduced the growth and survival of human B/myeloid MPAL cells. Sirt1 knockout suppressed global gene activation in old HSCs, prominently the genes regulating protein synthesis and oxidative metabolism, which may involve multiple downstream transcriptional factors. Our results demonstrate an unexpected role of SIRT1 in promoting HSC aging and age-dependent MPAL and suggest SIRT1 may be a new therapeutic target for modulating functions of aging HSCs and treatment of MPAL.


Statistics
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Data analysis
We used open source software for microarray data collection and analysis including Partek® Genomics Suite® (Partek Inc. release 6.12.0530), Gene Set Enrichment Analysis software (GSEA, v2.07) and Molecular Signature Database (MSigDB; v3.0). Graphpad Prizm 8.0 was used for statistical analysis and graphing for other data.
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Data
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Randomization Lethally irradiated recipient mice were randomly distributed among study groups.

Blinding
The group allocation was not blinded to the investigators as we didn't have enough personnel to carry out the double-blinded study.

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Flow Cytometry
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Methodology
Sample preparation Blood and bone marrow samples were harvested from mice, processed and then stained with antibodies as detailed in the methods.

Cell population abundance
The abundance of cell population varied largely depending on the cell fractions to be studied as detailed in the manuscript. The purity of SP fractions was determined by post-sort flow analysis to be higher than 97% (Wang Z. et al Stem Cell 2015;33:3437-3451) Gating strategy We gated most live mononucleated cells on the starting SSC/FSC plots. The boundary for "positive" and "negative" staining fractions was defined by the clear gap between two. More detailed gating strategies have been shown previously in Wang Z. et al Stem Cell 2015;33:3437-3451. Tick this box to confirm that a figure exemplifying the gating strategy is provided in the Supplementary Information.